The major components of a screenplay are action
and dialogue, with the "action" being "what we see happening" and
"dialogue" being "what we hear" (i.e., what the characters utter).
The characters, when first introduced in the screenplay, may also
be described visually. Screenplays differ from traditional
literature conventions in ways described below; however,
screenplays may not involve emotion-related descriptions and other
aspects of the story that are, in fact, visual within the
end-product.

Screenplays in print are highly formal,
conforming to font and margin specifications designed to cause one
page of screenplay to correspond to approximately one minute of
action on screen; thus screen directions and descriptions of
location are designed to occupy less vertical space than dialogue,
and various technical directions, such as settings and camera
indication are set apart from the text with capital letters and/or
indentation. Professional screenplays are always printed in
12-point Courier,
or another fixed-width font that appears like typewriter type.

In the United States, the Writers
Guild of America (WGA) has final control on whom may be awarded
screenwriting
credit for a screenplay in a union
production. The WGA is one of several organizations in the U.S. and
worldwide which recognize screenplays with awards.

Writing on spec or assignment

Screenplays can be written
either on "spec" (speculative) or as assignment ("Commissioned").
The Variety language dictionary defines "spec script" as "a script
shopped or sold on the open market, as opposed to one commissioned
by a studio or production company."

Writing on assignment

Assignments are commissioned by
production companies or studios on the basis of pitches from
producers or writers, or literary properties they already own. Most
established writers do most of their work on assignment and will
only "spec" scripts which they think no-one will pay them to write,
or if they cannot find assignment work.

There are exceptions: some very famous writers
only write on spec because they know that they can get a better
price for their work this way. Other writers spec scripts that they
care deeply about so that they do not have to bend to the whims of
executives and producers.

An assignment may be for an original screenplay,
or for an adapted screenplay based on another work such as a novel,
film, short story, comic book, magazine article or, increasingly,
video game. It may also, however, be for a rewrite of an existing
script, and in fact this is how a large proportion of writers in
the modern studio system make their living. Rewriting scripts is an
art in itself and an extremely lucrative one at that: it is not
unknown for trusted writers in the higher echelons of the industry
to receive $200,000 a week (2004 numbers) for their efforts.
$50,000 per week is not uncommon.

Rewriting is difficult because executives often
have very clear ideas about what is wrong with a script; however,
they are usually unable to provide detailed prescriptions for ways
it can be fixed. This is not surprising, because screenwriting is
not the expertise of the executive, but of the screenwriter. The
writer is therefore usually expected to come up with a detailed
prescription for how the script can be improved, and then execute
this in a timely fashion. During the process of choosing a writer
to rewrite a script the executives may ask several writers for
their 'take' and choose the one who appears to have the greatest
likelihood of moving the script forward to the point where it may
be greenlit for
production.

Before 'going to script' a writer may be asked to
write a treatment,
an outline, or a
step
outline describing the script in various granularities of
detail. Some writers resist this process and will do anything to
avoid it and get down the writing the script itself; others embrace
the process and even deliver fairly elaborate treatments, the
so-called scriptments. It is fair to
say that producers tend to be wary of the former and pleasantly
surprised by the latter.

Spec scripts

Many Spec scripts (short for speculative) are
written independently by screenwriters in hopes of optioning
and eventually outright selling them to producers or studios. Other
spec scripts are written by writer-directors who plan to direct the
film themselves. Many so-called "art films" fall
into this latter category, whereas the former category tends to be
filled with "high
concept" scripts - mostly action or comedy, to which a star or
A-list director can be attached. However, most of the hundreds of
thousands of specialty scripts penned each year are written by
unknowns who are trying to attract attention and find it difficult
to generate the kind of “buzz” that more established scribes count
on to sell their scripts.

The development process

Once a studio has purchased or
commissioned a script, it goes through the process of revisions and
rewriting until all stakeholders are satisfied and ready to
proceed. It is not uncommon for a script to go through many, many
drafts on its journey to production. Very few scripts improve
steadily with each draft, and when a certain avenue has been
exhausted the writer will often be replaced and another brought in
to do a rewrite.

Occasionally it becomes impossible to satisfy all
such parties, and the project enters development
hell.

If a studio decides it does not wish to proceed
to production with the script, the project enters 'turnaround'.
Another studio may purchase the script from its original owner, but
the script is encumbered with the development costs the studio has
already incurred. At a certain point, it may simply be uneconomic
for anyone to purchase the script, even if it is a very good one.
This goes part of the way to explaining why some of the best
scripts in Hollywood remain unproduced.

The shooting script

Once a script has been approved for
production, camera directions and notes may be inserted by the
Director, and each scene is assigned a number to provide a
convenient way for the various production departments to reference
individual scenes. When a scene is omitted, its number is retained
labeled with "OMITTED", so that it won't be assigned to any newly
added scenes.

When the shooting script is distributed, its
pages are locked, meaning that any subsequent revisions will apply
to the first set of revision pages. When revisions are distributed,
the pages are swapped into the outstanding drafts, and the script
is once again locked. The process is repeated for each new round of
revisions.

Each round of revisions is distributed on
different colored paper. The progression of colors varies from one
production to the next. Since rewrites often continue throughout
principal photography, most shooting scripts evolve into a rainbow
of pages.

Transcripts

A screenplay is different from a transcript. A
transcript is simply a copy of what dialogue finally appeared
onscreen, without regard to the original script, the stage
directions or action. A full post-production transcript may also
include descriptions of the action on-screen, but since it is
generally not written by a professional writer but either a
production assistant or a fan, it may not be particularly
entertaining to read.

Many published screenplays available at
booksellers or downloaded from the internet are in fact glorified
post-production transcripts rather than shooting scripts.
Transcripts and screenplays often differ radically because scenes
are frequently re-ordered or dropped entirely during the editing
process. Moreover, actors may change lines or simply improvise
dialog, and many directors will make their own changes to the
script on the fly during rehearsal or shooting.

It can be extremely revealing to compare a
shooting script with the film as finally distributed.

Screenwriting software

Detailed computer programs are
designed specifically for screenplays, and many have templates for
teleplays and stageplays. These programs have been designed to
create industry standard screenplays and are used by professional
screenwriters. What should be remembered is that all such software
is an aid in the formatting of a screenplay and not the actual
creation of it. A number of these programs offer access to online
screenwriter communities where feedback from fellow screenwriters
is available. Some examples of screenwriting software are: Celtx, DreamaScript,
Final
Draft & Montage.
Screenwriting software is also becoming available as web
applications, accessible from any computer, and on mobile
devices, for writing anywhere.